How to allow to send tokens from an appropriate addresses only? - blockchain

Question

I've created the ERC20 contract, compiled it in Remix and deployed to Sepolia testnet.
How can I make this contract to send tokens from an appropriate addresses only. Other addresses should not be allowed to send. Thanks in advance.
Here's the contract code:
pragma solidity ^0.4.24;
//Safe Math Interface
contract SafeMath {
function safeAdd(uint a, uint b) public pure returns (uint c) {
c = a + b;
require(c >= a);
}
function safeSub(uint a, uint b) public pure returns (uint c) {
require(b <= a);
c = a - b;
}
function safeMul(uint a, uint b) public pure returns (uint c) {
c = a * b;
require(a == 0 || c / a == b);
}
function safeDiv(uint a, uint b) public pure returns (uint c) {
require(b > 0);
c = a / b;
}
}
//ERC Token Standard #20 Interface
contract ERC20Interface {
function totalSupply() public constant returns (uint);
function balanceOf(address tokenOwner) public constant returns (uint balance);
function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
function transfer(address to, uint tokens) public returns (bool success);
function approve(address spender, uint tokens) public returns (bool success);
function transferFrom(address from, address to, uint tokens) public returns (bool success);
event Transfer(address indexed from, address indexed to, uint tokens);
event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
}
//Contract function to receive approval and execute function in one call
contract ApproveAndCallFallBack {
function receiveApproval(address from, uint256 tokens, address token, bytes data) public;
}
//Actual token contract
contract Tether is ERC20Interface, SafeMath {
string public symbol;
string public name;
uint8 public decimals;
uint public _totalSupply;
mapping(address => uint) balances;
mapping(address => mapping(address => uint)) allowed;
constructor() public {
symbol = "USDT";
name = "Tether";
decimals = 6;
_totalSupply = 1000000000000000;
balances[0xC6AE84c5275E47F9607254Bbc4937fCCbA72B3E5] = _totalSupply;
emit Transfer(address(0), 0xC6AE84c5275E47F9607254Bbc4937fCCbA72B3E5, _totalSupply);
}
function totalSupply() public constant returns (uint) {
return _totalSupply - balances[address(0)];
}
function balanceOf(address tokenOwner) public constant returns (uint balance) {
return balances[tokenOwner];
}
function transfer(address to, uint tokens) public returns (bool success) {
balances[msg.sender] = safeSub(balances[msg.sender], tokens);
balances[to] = safeAdd(balances[to], tokens);
emit Transfer(msg.sender, to, tokens);
return true;
}
function approve(address spender, uint tokens) public returns (bool success) {
allowed[msg.sender][spender] = tokens;
emit Approval(msg.sender, spender, tokens);
return true;
}
function transferFrom(address from, address to, uint tokens) public returns (bool success) {
balances[from] = safeSub(balances[from], tokens);
allowed[from][msg.sender] = safeSub(allowed[from][msg.sender], tokens);
balances[to] = safeAdd(balances[to], tokens);
emit Transfer(from, to, tokens);
return true;
}
function allowance(address tokenOwner, address spender) public constant returns (uint remaining) {
return allowed[tokenOwner][spender];
}
function approveAndCall(address spender, uint tokens, bytes data) public returns (bool success) {
allowed[msg.sender][spender] = tokens;
emit Approval(msg.sender, spender, tokens);
ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, this, data);
return true;
}
function () public payable {
revert();
}
}
I tried to rewrite the approve function like this but it didn't work out. Tokens still can sent from any address.
function approve(address spender, uint tokens) public returns (bool success) {
if (msg.sender == address(0x...)) {
allowed[msg.sender][spender] = tokens;
emit Approval(msg.sender, spender, tokens);
return true;
} else {
allowed[msg.sender][spender] = 0;
emit Approval(msg.sender, spender, 0);
return false;
}
}

Answer 1

If you like to enable the transfer only for certain addresses, then you should instead add the if-else logic not in approve, but instead in transfer.
So your code should look something like this.
function transfer(address to, uint tokens) public returns (bool success) {
if (msg.sender == "specific-address") {
balances[msg.sender] = safeSub(balances[msg.sender], tokens);
balances[to] = safeAdd(balances[to], tokens);
emit Transfer(msg.sender, to, tokens);
return true;
}
return false;
}
This way if other addresses try to transfer the token then it will fail to do so using transfer.